Totally sheltered, totally dependent, fetuses inhabit an environment entirely apart from that of any other stage of life. They have, as a result, unique properties. One fetal surgeon and his research team are applying those properties to diabetic wounds — but the implications of their work go far deeper than skin.
It's a fact known to fetal surgeons like Kenneth Liechty, MD, that fetuses can heal perfectly, without scars. Surgeries, heart attacks, tears and contusions to organs, tendons, skin — fetuses weather them all and come out like new.
"You look at animals like the salamander that can regrow limbs or the zebrafish that can regenerate tissue," he notes, "and really the only real mammalian example of that is the fetus."
"The question is, how do you fetalize the adult?"
Kenneth Liechty, MD
Director, Pediatric Surgery Basic and Translational Research
That's always fascinated Dr. Liechty. Early in his career, he and colleagues observed that preterm infants were more susceptible than full-term neonates to overwhelming sepsis, suggesting a difference in the fetal inflammatory response. From an evolutionary perspective, that would make sense. A fetus's priority is to grow and make new tissue.
“Once you’re out of the womb, it’s about getting the wound closed before you die of infection.”
Fetal healing and the diabetic wound
That big, brisk inflammatory response is great if you're a hunter-gatherer, not so good if you have, say, a chronically inflammatory condition. Even worse if you have one like diabetes, which also saps the immune system, weakens skin, damages nerves and, because it often correlates with obesity, puts extra pressure on feet.
"The bacterial load of diabetic skin is 40 times higher than healthy skin," says Dr. Liechty. "So you have skin that's weaker and easier to injure, you can't feel it when you're injured, and then there's a bunch of bacteria sitting around."
"It creates an environment so inflammatory, so hostile," says University of Colorado School of Medicine regenerative biologist Carlos Zgheib, PhD, a researcher in Dr. Liechty's lab, "that cells are not going to be able to proliferate and close that wound."
More than 30 million people in the U.S. have diabetes, and 20 percent of them have non-healing wounds. That's on top of 84 million more with prediabetes. At last count, the rate of diabetic amputations was around 73,000 a year.
"So the question is," says Dr. Liechty, "how do you fetalize the adult?"
The role of reactive oxygen species in inflammation
When the skin breaks, macrophages invade the area and start cranking out reactive oxygen species, volatile compounds that damage cells around them by stripping elements of their DNA. That damages microbes, but it also damages the surrounding tissue.
Materials engineer and biochemist Sudipta Seal, PhD, Dr. Liechty's collaborator at the University of Central Florida, figured out years ago that a rare earth metal called cerium oxide could bind reactive oxygen species. At the time it was used primarily in catalytic converters and jewelry polish. Dr. Seal observed that, in the form of nanoparticles known as nanoceria, it could slow the progression of macular degeneration. Drs. Liechty and Zgheib discovered it could promote wound healing.
But it didn’t work on diabetic wounds.
At the same time, Dr. Liechty's research team was working with microRNAs, non-coding RNAs that regulate gene expression. They'd been used in cancer research, but Dr. Liechty's team was the first to use them to recreate the inflammatory conditions of the womb by shutting down pro-inflammatory interleukins 6 and 8.
Conjugating nanoceria to microRNA
The problem was that oxidative stress signals more inflammation. Diabetic wounds were so persistent that, as soon as the microRNA wore off, oxidative stress would stoke the inflammation again.
It was when they combined the two that everything changed.
"It was like a miracle," says Dr. Zgheib. "In the animal model, we corrected diabetic healing to the normal rate."
The discovery earned Dr. Zgheib the American College of Surgeons' Excellence in Research Award last year, with publication in that group's journal. The research team hopes to start Phase 1 clinical trials this year.
"You'd worry maybe it's just a superficial closure, not functionally healed," adds Dr. Liechty. "We've shown it's actually better. Diabetic skin at baseline is weak. When we test our wound closures, they're stronger."
Delivering nanoceria and microRNA to diabetic wounds
The team is now refining how the combination of nanoceria and microRNA, which Dr. Zgheib calls "the conjugate," gets into the wound. Initially they injected it. That's fine for animal studies, but they knew sticking needles into open wounds would be a tall order for actual patients.
Better would be a topical application, maybe a cream or a gel. Something you could do right at home. For that, they're partnering with Colorado School of Mines bioengineer Melissa Krebs, PhD, who developed a water-based gel that not only to infuses the conjugate into the wound but acts as a bandage with a time-release.
Dr. Krebs, who also partners with a team of Children's Colorado researchers looking at growth plate regeneration, specializes in synthetic gels that mimic the conditions of life. That's important, because when you're infusing an anti-inflammatory agent into a wound, the last thing you want to do is provoke more inflammation.
For the conjugate, she developed a delivery system using zwitterions, monomers with complementary positive and negative sides that link up to form long polymer chains. Dissolved in water, these polymers will evenly disperse — so much so that the drug pretty much bleeds out right away.
"You make that mix in a freezer, though," says Dr. Krebs, "and the polymerization still occurs, but as it's occurring the water is freezing, so the ice is clustering, and that makes the polymer cluster. It compartmentalizes the ice and the polymer, so you get a denser polymer structure that can physically entrap the drugs we're putting in."
The natural pressure of daily life then squeezes the drug out through a kind a labyrinth of polymers for an impressively even, sustained delivery.
"It keeps the area moist and over time releases the conjugate into the wound," says Dr. Liechty. "We're seeing healing times along the same lines as injection."
Even better, it protects the wound while it heals.
"We can get up to four months of sustained protein release," says Dr. Krebs. "It keeps in moisture and lets the area knit together underneath. After a while, after the tissue heals, our gel will basically just pop off. It's like a smart Band-Aid."
Leveraging nanoparticles to prevent diabetic wounds
Even better than faster healing is a wound that never occurs. For that the team is developing another nanoparticle, this one derived from silk.
"You think about silk sutures, they're strong. They don't break," says Dr. Zgheib. "We found this nanosilk solution we make in the lab actually strengthens diabetic skin. The idea is, imagine a spray bottle. You spray it on, give it a minute to dry off, that's it."
It's a kind of invisible armor that could protect skin ulcers of all kinds, from diabetic wounds to pressure injuries in hospitals or nursing homes. It's also effective, coupled with Dr. Krebs' gel, for protecting wounds as they heal.
Changing the mechanism of healing
The implications of their work plumb deeper than skin. With its dual mechanisms of attack, the conjugate has potential to revise the mechanism of healing all over the body, wherever inflammation exists. Dr. Liechty's collaborators at the University of Pennsylvania found it can prevent cardiac remodeling after a heart attack. Others showed it can decrease fibrosis and promote lung function. More studies are in the works.
"Hopefully we'll have this online by the time I have heart disease," Dr. Liechty says, only half-joking. "It's really the future."